A good water-based system for filling wood grain is to make a brushable slurry of spackling compound and water, then brush it onto the wood. Make this as "dry" as possible, because some have reported problems with passing water even close to wood! But if the wood skin is not too thin, I have never had a problem with it. Once the goop is dry, take it OUTSIDE or in a WELL VENTILATED area to sand all of it off (leaving behind only that which is filling the pores). If you have ever sanded drywall, you know why it goes outside. Now you will need to seal this, so I use flooring-grade clear water-based Varthane. You will get 'hunnerd-eleven' opinions about the urethane, too! An alternative is a can of auto primer or other primer. You will want to apply it in some way which does not "lift" your filler out. I airbrushed the clear over the sealer (see pic). Whatever floats your boat! Good luck, Dzl